Efficiently joining over interval ranges in SQL

Question

Suppose I have two tables as follows (data taken from this SO post):

Table d1:

 x start end
 a     1   3
 b     5  11
 c    19  22
 d            


        

Answer 1

Not sure how it all works out internally, but depending on the situation I would advice to play around with a table that 'rolls out' all the values from d1 and then join on that one. This way the query engine can pinpoint the right record 'exactly' instead of having to find a combination of boundaries that match the value being looked for.

e.g.

x value
a  1
a  2
a  3
b  5
b  6
b  7
b  8
b  9
b 10
b 11
c 19 etc..

given an index on the value column (**), this should be quite a bit faster than joining with the BETWEEN start AND end on the original d1 table IMHO.

Off course, each time you make changes to d1, you'll need to adjust the rolled out table too (trigger?). If this happens frequently you'll spend more time updating the rolled out table than you gained in the first place! Additionally, this might take quite a bit of (disk)space quickly if some of the intervals are really big; and also, this assumes we don't need to look for non-whole numbers (e.g. what if we look for the value 3.14 ?)

(You might consider experimenting with a unique one on (value, x) here...)